The present invention is directed to a diaphragm pumping apparatus. The invention is more specifically directed to an improved construction of a reciprocating air driven double acting diaphragm pump.
Air driven diaphragm pumps are widely applied in construction and industrial applications. The pumps can be made to be durable and reliable and they have the major advantage that they can handle a wide variety of fluids to be pumped. Regardless of the application to which such a pump is put, the amount of energy consumption associated with operating the pump and the ease with which the pump can be maintained are two matters of great concern to its user.
Many of the prior art diaphragm pumps show little attention to these considerations. Examples of such pumps include U.S. Pat. No. 3,838,946 issued to Schall, U.S. Pat. No. 4,008,984 issued to Scholle and U.S. Pat. No. 4,247,264 issued to Wilden. These three patents disclose air driven diaphragm pump mechanisms. Each of them include an opposing set of pump chambers linked by a solid shaft. In all three designs, a relatively large amount of compressed air must be supplied during each cycle to the control and supply lines which feed the pump chambers to operate the pump. The energy efficiency of such a pump relates directly to the quantity of air consumption with each pump stroke. Therefore, a well designed diaphragm pump would minimize this quantity.
Of even greater concern to the pump operator is the effort required to perform routine maintenance and parts replacement. The ease of maintenance is greatly affected by the manner in which the individual pump components are assembled and held in place. Of particular concern is the accessibility of the pumping chambers and diaphragms. The diaphragms, which alternately expand and contract the pumping chamber, undergo numerous flexure cycles and significant abrasion during their operation, and thus must periodically be replaced or repaired. Consequently, the ability to access the pumping chamber and the individual diaphragms to perform this maintenance has a great impact on the ease or difficulty of maintenance of air driven diaphragm pumps.
The prior art teaches a variety of approaches to the maintenance problem. The Scholle patent shows a pump in which the operating chambers and supporting structure are provided in a single casting. End caps secured to the casting are removable to replace the pump diaphragms located near the outer ends of the pump.
The Schall patent shows a pump assembly which, when viewed from above, comprises two pump chambers surrounded by plumbing. That structure rests on a support beam which is co-axial with the pump chambers. To replace a pump chamber diaphragm, the bolts holding that pump chamber are removed and the surrounding pipes are disconnected.
The Wilden design also points up the problems inherent in pump disassembly and replacement of the diaphragm. As a solution, Wilden adopts a pump configuration which completely disassembles with the removal of four tie rods.
In addition to efficiency and maintenance considerations, further design concerns arise from diaphragm pumps being operated in dirty environments. ln such applications, it is important that the pump design guard against the effects of the inevitable air supply contamination. Even slight amounts of dirt or oil in the air supply easily can interfere with the typical control systems or air supplies which operate the diaphragm pump. Unless care is taken in the design of the pump to accommodate such environments, the reliability and smooth operation of the pump will suffer.
Many industrial process applications call upon diaphragm pumps to supply a fluid substance to a process location on demand. For example, the pump might be used to pump glue to a particular application point in a process line. In such an application, all of the operational and design concerns mentioned above are important. In addition, it becomes very important under such circumstances that the pump provide smooth consistent operation even when being operated slowly. Because of transient conditions that occur when the reciprocating shaft of the pump reverses directions, many air driven diaphragm pumps do not provide smooth consistent operation at low speeds. Such diaphragm pumps are also susceptible to binding when operated under conditions of low operating pressure due to potential misalignment between the single shaft connecting the pump chambers and the bearing surfaces upon which the shaft rides. Furthermore, such pumps may be prone to pressure and flow surges resulting from dirt or oil in their air-operated control system or resulting from the lag time for shaft reversal in the case of designs which place the air supply control valve at a significant distance from the pump chambers. In a process line in which the pump is supplying a liquid such as glue, for example, such pressure and flow rate surges will cause surges in the glue flow, an obviously unacceptable condition. A well designed diaphragm pump must take all of these factors into account.